This study will characterize the natural history of aortic regurgitation from the hemodynamic point of view. The objective is to provide data for the formulation of rational criteria for the selection of therapy for patients with aortic regurgitation. Present treatment criteria are based primarily on symptoms - if a patient is significantly limited symptomatically, aortic valve replacement is recommended. However, a recent study carried out by the principal investigator demonstrated that the long-term prognosis after aortic valve replacement is related to the pre-operative left ventricular function rather than the severity of symptoms. This suggested that criteria for aortic valve replacement should be reformulated to include left ventricular function. Approximately 75 patients who have severe aortic regurgitation but who are not presently symptomatic will be studied. At the initial intake into the study hemodynamic and clinical data will be assembled. The procedures to be performed will inculde: Cardiac catheterization, Exercise testing, Echocardiography, and ECG gated radionucleide cardiac blood pool scanning. Once the baseline data is assembled the patients will be followed until the development of significant symptoms with periodic noninvasive outpatient assessments of left ventricular function. The relationship between clinical and hemodynamic data to prognosis will be assessed. The results of the study will provide a data base on which criteria for treatment of aortic regurgitation may be formulated scientifically.